Measure health with motion

// Grab authorization to read and share sixMinuteWalkTestDistance type

let healthStore = HKHealthStore()
let types: Set = [
    HKObjectType.quantityType(forIdentifier: .sixMinuteWalkTestDistance)!
]

healthStore.requestAuthorization(toShare: types, read: types) { _, _ in }

// Recalibrate estimate

let healthStore = HKHealthStore()
let sixMinuteWalkType = HKSampleType.quantityType(forIdentifier: .sixMinuteWalkTestDistance)!

if sixMinuteWalkType.allowsRecalibrationForEstimates {

    healthStore.recalibrateEstimates(sampleType: sixMinuteWalkType, date: surgeryDate) { 
        (success, error) in
        // Handle error
    }

}

// Get authorized

let types: Set = [
    HKObjectType.quantityType(forIdentifier: .walkingSteadiness)!
]

healthKitStore.requestAuthorization(toShare: nil, read: types) { _, _ in }

// Construct a query for most recent walkingSteadiness score

let steadinessType = HKObjectType.quantityType(forIdentifier: .walkingSteadiness)
let sortByEndDate = NSSortDescriptor(key: HKSampleSortIdentifierEndDate, ascending: false)

let query = HKSampleQuery(sampleType: steadinessType,
                          predicate: nil,
                          limit: 1,
                          sortDescriptors: [sortByEndDate]) { (query, samples, error) in

    if let sample = samples?.first as? HKQuantitySample{

        let recentScore = sample.quantity.doubleValue(forUnit: .percentUnit)

        updateStatus(score: recentScore)
    }
}

self.healthStore.execute(query)

// Construct a query for most recent walkingSteadiness classification

let steadinessType = HKObjectType.quantityType(forIdentifier: .walkingSteadiness)

let query = HKSampleQuery(sampleType: steadinessType,
                          predicate: nil,
                          limit: 1,
                          sortDescriptors: nil) { (query, samples, error) in

    if let sample = samples?.first as? HKQuantitySample{
        
        let recentScore = sample.quantity.doubleValue(forUnit: .percentUnit)

        // Use HealthKit API to classify a value as OK, Low, or Very Low
        let recentClassification = HKAppleWalkingSteadinessClassification(for: walkingSteadiness.quantity)

        updateStatus(classification: recentClassification, score: recentScore)
    }
}

self.healthStore.execute(query)

// Get authorized

let types: Set = [
    HKObjectType.categoryType(forIdentifier: .walkingSteadinessEvent)!
]

healthKitStore.requestAuthorization(toShare: nil, read: types) { _, _ in }

// Watch for walkingSteadiness notifications

let notificationType = HKCategoryType.categoryType(forIdentifier: .appleWalkingSteadinessEvent)!

let query = HKObserverQuery(sampleType: notificationType, predicate: nil) { 
    (query, completionHandler, errorOrNil) in
    
    if let error = errorOrNil {
        // Properly handle the error.
        return
    }

    promptCheckupForNotification()

    completionHandler()
}

self.healthStore.execute(query)

// Query samples from HealthKit

// Look back 6 weeks
let end = Date()
let start = Calendar.current.date(byAdding: .week, value: -6, to: end)

let datePredicate = HKQuery.predicateForSamples(withStart: start, end: end, options: [])

// Query walking steadiness
let steadinessType = HKObjectType.quantityType(forIdentifier: .walkingSteadiness)
let sortByEndDate = NSSortDescriptor(key: HKSampleSortIdentifierEndDate, ascending: false)

let query = HKSampleQuery(sampleType: steadinessType,
                          predicate: sortByEndDate,
                          limit: nil,
                          sortDescriptors:[sortByEndDate]) { (_, samples, _) in

    detectTrends(samples)
}
self.healthStore.execute(query)